Mybatis之Spring与Mybatis的事物transaction

克虏伯

发布于 2019-10-28 10:05:08

1.1K0

发布于 2019-10-28 10:05:08

mybatis-3.4.6.release, mybatis-spring-1.3.2.release.

List-1

<!-- 配置mybatis的sqlSessionFactory -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <!-- 自动扫描mappers.xml文件 -->
    <!--<property name="mapperLocations" value="classpath:com/mjduan/project/mapper/*.xml"/>-->
    <!-- mybatis配置文件 -->
    <property name="configLocation" value="mybatis-config.xml"/>
</bean>

<!-- DAO接口所在包名，Spring会自动查找其下的类 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.mjduan.project.mapper"/>
    <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
</bean>

先来看SqlSessionFactoryBean，它需要一个dataSource，还是就是mybatis的xml配置文件。

SqlSessionFactoryBean类实现了InitializingBean接口，了解SpringIOC的话，就知道InitializingBean的作用了。来看InitializingBean的afterPropertiesSet()，afterPropertiesSet()调用buildSqlSessionFactory()生成SqlSessionFactory，

List-2

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
    Configuration configuration;

    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
        configuration = this.configuration;
        if (configuration.getVariables() == null) {
        configuration.setVariables(this.configurationProperties);
        } else if (this.configurationProperties != null) {
        configuration.getVariables().putAll(this.configurationProperties);
        }
    } else if (this.configLocation != null) {
        xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
        configuration = xmlConfigBuilder.getConfiguration();
    } else {
        if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
        }
        configuration = new Configuration();
        if (this.configurationProperties != null) {
        configuration.setVariables(this.configurationProperties);
        }
    }

    if (this.objectFactory != null) {
        configuration.setObjectFactory(this.objectFactory);
    }

    if (this.objectWrapperFactory != null) {
        configuration.setObjectWrapperFactory(this.objectWrapperFactory);
    }

    if (this.vfs != null) {
        configuration.setVfsImpl(this.vfs);
    }

    if (hasLength(this.typeAliasesPackage)) {
        String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        for (String packageToScan : typeAliasPackageArray) {
        configuration.getTypeAliasRegistry().registerAliases(packageToScan,
                typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
        }
        }
    }

    if (!isEmpty(this.typeAliases)) {
        for (Class<?> typeAlias : this.typeAliases) {
        configuration.getTypeAliasRegistry().registerAlias(typeAlias);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Registered type alias: '" + typeAlias + "'");
        }
        }
    }

    if (!isEmpty(this.plugins)) {
        for (Interceptor plugin : this.plugins) {
        configuration.addInterceptor(plugin);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Registered plugin: '" + plugin + "'");
        }
        }
    }

    if (hasLength(this.typeHandlersPackage)) {
        String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        for (String packageToScan : typeHandlersPackageArray) {
        configuration.getTypeHandlerRegistry().register(packageToScan);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");
        }
        }
    }

    if (!isEmpty(this.typeHandlers)) {
        for (TypeHandler<?> typeHandler : this.typeHandlers) {
        configuration.getTypeHandlerRegistry().register(typeHandler);
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Registered type handler: '" + typeHandler + "'");
        }
        }
    }

    if (this.databaseIdProvider != null) {//fix #64 set databaseId before parse mapper xmls
        try {
        configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
        } catch (SQLException e) {
        throw new NestedIOException("Failed getting a databaseId", e);
        }
    }

    if (this.cache != null) {
        configuration.addCache(this.cache);
    }

    if (xmlConfigBuilder != null) {
        try {
        xmlConfigBuilder.parse();

        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");
        }
        } catch (Exception ex) {
        throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
        } finally {
        ErrorContext.instance().reset();
        }
    }
    //这里transactionFactory使用SpringManagedTransactionFactory，在获取connection时会用到
    if (this.transactionFactory == null) {
        this.transactionFactory = new SpringManagedTransactionFactory();
    }
    //通过environment来传递
    configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));

    if (!isEmpty(this.mapperLocations)) {
        for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
            continue;
        }

        try {
            XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                configuration, mapperLocation.toString(), configuration.getSqlFragments());
            xmlMapperBuilder.parse();
        } catch (Exception e) {
            throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
        } finally {
            ErrorContext.instance().reset();
        }

        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
        }
        }
    } else {
        if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
        }
    }

    return this.sqlSessionFactoryBuilder.build(configuration);
}

List-2中的方法内容很多，但是整个在做的就是生成Configuration。

我们需要注意的点是this.transactionFactory = new SpringManagedTransactionFactory()，这是mybatis和spring联系到一起的点。

再来看MapperScannerConfigurer，这个类实现了BeanDefinitionRegistryPostProcessor接口，在postProcessBeanDefinitionRegistry方法中实例化了个ClassPathMapperScanner，之后scan->doScan:

List-3

  private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (GenericBeanDefinition) holder.getBeanDefinition();

      if (logger.isDebugEnabled()) {
        logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
          + "' and '" + definition.getBeanClassName() + "' mapperInterface");
      }

      // the mapper interface is the original class of the bean
      // but, the actual class of the bean is MapperFactoryBean
      definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
      //设置MapperFactoryBean类型
      definition.setBeanClass(this.mapperFactoryBean.getClass());

      definition.getPropertyValues().add("addToConfig", this.addToConfig);

      boolean explicitFactoryUsed = false;
      if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
        definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
        explicitFactoryUsed = true;
      } else if (this.sqlSessionFactory != null) {
        //设置属性引用SqlSessionFactory  
        definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
        explicitFactoryUsed = true;
      }

      if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
        if (explicitFactoryUsed) {
          logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
        }
        definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
        explicitFactoryUsed = true;
      } else if (this.sqlSessionTemplate != null) {
        if (explicitFactoryUsed) {
          logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
        }
        definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
        explicitFactoryUsed = true;
      }

      if (!explicitFactoryUsed) {
        if (logger.isDebugEnabled()) {
          logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
        }
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
    }
  }

List-3中将扫描到的mapper接口，封装为MapperFactoryBean，且将SqlSessionFactory设置为其属性。

MapperFactoryBean类继承SqlSessionDaoSupport，setSqlSessionFactory的方法在父类SqlSessionDaoSupport中，如下List-4，利用SqlSessionTemplate初始化sqlSession。

List-4

public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (!this.externalSqlSession) {
        this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
    }
}

来看SqlSessionTemplate的构造方法，如下List-5

List-5

  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
    notNull(executorType, "Property 'executorType' is required");

    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }

SqlSessionTemplate实现了接口SqlSession，SqlSessionTemplate内部所有的方法实现都委托给sqlSessionProxy来实现的，sqlSessionProxy是JDK动态代理的，来看SqlSessionInterceptor：

List-6

  private class SqlSessionInterceptor implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

List-6中首先获得SqlSession，如果SqlSession不存在，则通过sessionFactory.openSession来创建一个。

List-7

  public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
    notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);

    SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

    SqlSession session = sessionHolder(executorType, holder);
    if (session != null) {
      return session;
    }

    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Creating a new SqlSession");
    }

    session = sessionFactory.openSession(executorType);

    registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);

    return session;
  }

sessionFactory.openSession()->openSessionFromDataSource()，获取Environemnt，之后从Environment中获取TransactionFactory——List-2中的SpringManagedTransactionFactory, newTransaction()返还的是SpringManagedTransaction。

List-8

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

final Executor executor = configuration.newExecutor(tx, execType)，默认情况下是SimpleExecutor，现在SqlSession有了，回到List-6的method.invoke()，即实际调用时这个方法会被调用，以update为例，看SimpleExecutor的doUpdate方法

List-9

  @Override
  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.update(stmt);
    } finally {
      closeStatement(stmt);
    }
  }

来看prepareStatement()，如下List-10，通过transaction.getConnection来获取Connection，而这个transaction就是SpringManagedTransaction，

List-10

  private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    Connection connection = getConnection(statementLog);
    stmt = handler.prepare(connection, transaction.getTimeout());
    handler.parameterize(stmt);
    return stmt;
  }

  protected Connection getConnection(Log statementLog) throws SQLException {
    Connection connection = transaction.getConnection();
    if (statementLog.isDebugEnabled()) {
      return ConnectionLogger.newInstance(connection, statementLog, queryStack);
    } else {
      return connection;
    }
  }

SpringManagedTransaction中getConnection会调用openConnection，如下List-11，

List-11

  private void openConnection() throws SQLException {
    this.connection = DataSourceUtils.getConnection(this.dataSource);
    this.autoCommit = this.connection.getAutoCommit();
    this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);

    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug(
          "JDBC Connection ["
              + this.connection
              + "] will"
              + (this.isConnectionTransactional ? " " : " not ")
              + "be managed by Spring");
    }
  }

通过DataSourceUtils.getConnection()来获取Connection->doGetConnection()，从TransactionSynchronizationManager中获取ConnectionHler，如果是null，则通过dataSource来得到一个Connection；如果不为null，且已经开启事物，则直接返回connectionHolder中的connection。

List-12

public static Connection doGetConnection(DataSource dataSource) throws SQLException {
    Assert.notNull(dataSource, "No DataSource specified");
    ConnectionHolder conHolder = (ConnectionHolder)TransactionSynchronizationManager.getResource(dataSource);
    if (conHolder == null || !conHolder.hasConnection() && !conHolder.isSynchronizedWithTransaction()) {
        logger.debug("Fetching JDBC Connection from DataSource");
        Connection con = dataSource.getConnection();
        if (TransactionSynchronizationManager.isSynchronizationActive()) {
            logger.debug("Registering transaction synchronization for JDBC Connection");
            ConnectionHolder holderToUse = conHolder;
            if (conHolder == null) {
                holderToUse = new ConnectionHolder(con);
            } else {
                conHolder.setConnection(con);
            }

            holderToUse.requested();
            TransactionSynchronizationManager.registerSynchronization(new DataSourceUtils.ConnectionSynchronization(holderToUse, dataSource));
            holderToUse.setSynchronizedWithTransaction(true);
            if (holderToUse != conHolder) {
                TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
            }
        }

        return con;
    } else {
        conHolder.requested();
        if (!conHolder.hasConnection()) {
            logger.debug("Fetching resumed JDBC Connection from DataSource");
            conHolder.setConnection(dataSource.getConnection());
        }

        return conHolder.getConnection();
    }
}

TransactionSynchronizationManager通过ThreadLocal来保存ConnectionHolder，而Spring tx中也是通过这个类来对ConnectionHolder进行持有的。